1. Field of the Invention
The present invention relates to a mobile network communication technique and particularly to a method and apparatus for handoff in mobile network communication.
2. Description of the Related Art
In a wireless communication system, handoff between different systems such as a mobile phone and a wireless local area network (WLAN) is performed according to user's necessity.
FIG. 1 is a view showing an example of configuration of a wireless communication system concerned with handoff between systems. In FIG. 1, the reference numeral 1 designates an information contents server; 2, an IP network; 3, a home agent (HA) server of mobile IP (MIP); 8, a mobile station (MS); 5, a wireless local area network (WLAN) provided by a WLAN service provider; 4, a gateway (PDIF: Packet Data Inter-working Function) to the WLAN; 10, a WLAN access point (AP); 7, a mobile phone system (1×EvDO: 1× Evolution Data Only) network provided by a 1×EvDO service provider; 6, a gateway (PDSN: Packet Data Serving Node) to the 1×EvDO network; 13, a 1×EvDO access point (AP); and 15, a stationary network.
When the MS 8 needs to change the 1×EvDO access point to the WLAN access point or when the MS 8 needs to change the WLAN access point to the 1×EvDO access point, the MS 8 sends mobile IP registration information to the home agent HA and asserts a new PPP (Point to Point Protocol) session between the gateway PDIF/FA as a target and itself. If the old PPP session between the gateway PDSN and the MS at that time were held so continuously as not to be cleared until timeout, not only would a great deal of resources become wasteful but also there would be a bad influence on access to other mobile stations. In addition, as a more serious problem, a user must pay an excessive fee even though the network has been already changed to another wireless network.
U.S. Patent Application Publication 2004/0082330A has proposed a method for warranting handoff by using mobile IP between a wireless LAN (WLAN) and a third generation (3G) network. In the proposed method, it was possible to warrant handoff in one direction from the WLAN to the 3G network but it was impossible to warrant handoff in a reverse direction. This is because this proposed method gave no consideration about how to release network side not-yet-changed resources after changing the network.
That is, in the proposed method, when the MS changes one gateway to another wireless LAN gateway, the MS sends mobile IP registration information to the home agent HA and asserts a new PPP session between the gateway PDIF/FA as a target and itself. If the old PPP session between the gateway before handoff and the MS were held so continuously as not to be cleared until timeout, not only would a great deal of resources become wasteful but also there was a bad influence on access to other mobile stations. As a more serious problem, the user must pay an excessive fee.
In the process in which CDMA 1×EvDO is changed to the WLAN, the MS performs registration in the home agent through the PDIF again. The method about how to cut off PPP connection, that is, which of the MS and the PDSN cuts off PPP connection, has never been proposed.
If PPP connection is cut off by the MS, the PDSN sends deregistration information to the home agent. There is however a possibility that error may be caused by the home agent's deletion of registration information in the MS even in the case where the deregistration information reaches to the home agent so that the MS is registered in the home agent through the WLAN.